NP-Complete

Question 1
Consider the decision problem 2CNFSAT defined as follows: The decision problem 2CNFSAT is
A
NP-Complete.
B
solvable in polynomial time by reduction to directed graph reachability.
C
solvable in constant time since any input instance is satisfiable.
D
NP-hard, but not NP-complete.
       Theory-of-Computation       NP-Complete       Gate 2014 Set -03
Question 1 Explanation: 
Note: Out of Syllabus.
Question 2
Which of the following statements are TRUE?
1. The problem of determining whether there exists
   a cycle in an undirected graph is in P.
2. The problem of determining whether there exists
   a cycle in an undirected graph is in NP.
3. If a problem A is NP-Complete, there exists a 
   non-deterministic polynomial time algorithm to solve A.
A
1, 2 and 3
B
1 and 2 only
C
2 and 3 only
D
1 and 3 only
       Theory-of-Computation       NP-Complete       Gate 2013
Question 2 Explanation: 
Note: Out of syllabus.
1. Detecting cycle in a graph using DFS takes O(V+E)=O(V2)
Here, for complete graph E<= V2. So, It runs in polynomial time.
2. Every P-problem is NP because P subset of NP (P ⊂ NP)
3. NP – complete ∈ NP.
Hence, NP-complete can be solved in non-deterministic polynomial time.
Question 3
Which of the following problems is not NP-hard?
A
Hamiltonian circuit problem
B
The 0/1 Knapsack problem
C
Finding bi-connected components of a graph
D
The graph colouring problem
       Theory-of-Computation       NP-Complete       Gate-1992
Question 3 Explanation: 
Note: Out of syllabus.
There are 3 questions to complete.
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